The present invention generally relates to barrier systems that are fitted to various structural components of a building in order to afford protection from fire and heat. More particularly, the invention pertains to providing such protection for the base isolators that serve to both support a structure and reduce the transfer of seismic loads thereto.
Many buildings that are located in seismically active regions have been fitted or retrofitted with base isolator bearings. A plurality of such devices are positioned beneath a building so as to bear the full weight of the building, each one being fitted between the foundation and the structure it supports. A type of isolator in common use today consists of a large mass of rubber or rubber-like material that is sandwiched in between and permanently affixed to two steel plates. One such plate is securely bolted or otherwise attached to either a column extending upwardly from the foundation or directly to the foundation of the building, while the opposite plate is rigidly affixed to the vertical support column extending upwardly therefrom. Although such device is able to support tremendous weight loads and withstand sizeable shear loads and displacements, it is quite susceptible to heat and fire damage by virtue of its elastomeric constitution. Failure of such a structurally essential component could, of course, have catastrophic consequences, and it is therefore necessary to adequately protect each isolator from fire and heat damage. Moreover, it would also be most advantageous for any such protective measures to continue to provide adequate protection upon substantial shear displacement of the isolator, as a seismic event causing such shear displacement often renders the risk of fire acute.
Both active, as well as passive, systems have heretofore been employed in an effort to provide thermal protection for isolator bearings. An example of an active system is one that provides for the irrigation of the isolators during a fire. Disadvantages inherent in such an approach include the need to rely on fire detection and valve actuation equipment and, most importantly, the fact that an adequate water supply may not be available after a seismic event. The passive systems have to date been limited to a simple wrapping or layering of insulative materials about the bearing. A critical shortcoming inherent in such configuration is its inability to maintain or regain its integrity and hence its insulative efficacy upon substantial displacements of the bearing. A need therefore exists for a passive insulation system that is substantially unaffected by shear displacement.